下列动物中，体温恒定的动物是(　  　)

①鲸　②青蛙　③丹顶鹤　④鸭嘴兽　⑤大鲵　⑥扬子鳄　⑦鲫鱼

    A well-dressed man goes into a restaurant one day. He sits down at a table near the window. A waiter comes up to him and says, “Can I help you, sir?”

    The man says, “Can I see the menu?” “Certainly.”

    The man wants a good meal and he wants a lot of nice dishes. The waiter gets them for him. The man is having his meals. At this time, a boy comes in and sits beside the man. He asks the man to give him an ice cream. The man does so.

    Now the boy is eating his ice cream. The man says, “I go out for a newspaper.” The man goes out.  After the boy eats his ice cream up, he stands up and goes to the door.

    “Excuse me. Your father doesn't give the money for the meal and your ice cream,” The waiter stops him and says.

    “Father? You are wrong. He isn't my father. I don't know him. I meet him in the street. He says he will give me an ice cream if I come here at 12 o'clock.”

数a、b在数轴上的位置如图所示，化简：$\sqrt{{\left(a+1\right)}^2}+\sqrt{{\left(b-1\right)}^2}-\sqrt{{\left(a-b\right)}^2}$